Electrode for an electrochemical battery, electrochemical battery and method for producing an electrode

Abstract

The invention relates to an electrode (14) for an electrochemical battery (12), comprising a current collector foil (16) with a coating region (22) for an electrode coating (20), said coating region comprising an outer region (24) and a central region (26). An outer region (24) of the coated region (22) is closer to an outer edge (28) of the current collector foil (16) than a central region (26) of the coated region (22). The electrode coating (20) has, in the outer region (24), at least one electrolyte-conducting region (34), in which an electrolyte (38) of the electrochemical battery (12) diffuses at a higher speed than in the electrode coating (20) outside the electrolyte-conducting region (34). The invention further relates to an electrochemical battery (12) and to a method for producing an electrode.

Description

Technical Field

[0001] The invention relates to an electrode for an electrochemical accumulator, an electrochemical accumulator comprising such an electrode and a method for producing an electrode. Background Art

[0002] Electrochemical accumulators are energy storage devices based on electrochemistry which are in particular rechargeable and suitable for storing electrical energy and supplying it to electrical consumers, for example in a vehicle.

[0003] The decisive factors for the performance of electrochemical accumulators are the achievable energy density, the service life and the usable charge and discharge rates, the latter being of particular importance in vehicle applications and should be as high as possible. However, the usable charge and discharge rates are limited by various effects, in particular by the temperature changes that can be expected during the charging and discharging process and by aging effects.

[0004] Electrochemical accumulators have at least two different electrodes, namely a positive electrode (cathode) and a negative electrode (anode). Each of these electrodes has at least one active material, optionally together with additives such as electrode binders and conductivity additives, which is applied to a conductive support of the respective electrode. As conductive supports, solid, non-porous and fixed current collector foils made of aluminum (for positive electrodes) or copper (for negative electrodes), also referred to in technical parlance as “solid foils”, are used in particular. Such current collector foils are impermeable to gases and liquid electrolytes.

[0005] The electrodes are in particular in the form of electrode coils (also called “jelly rolls”) for use in electrochemical batteries, wherein a separator is arranged between each cathode and anode for electrical insulation.

[0006] During the production of electrochemical accumulators, it is necessary to saturate the electrode coil with electrolyte after it has been inserted into the housing, wherein a certain exposure time is required in order to ensure sufficient and uniform wetting of the inner cavities of the electrode up to the interface.

[0007] It has been found that complete wetting is generally not possible in known electrochemical accumulators. In particular, it can be observed in the center of the electrochemical accumulator that, in the most unfavorable case, the center remains essentially dry. However, the areas of the electrochemical accumulator that are not soaked by the electrolyte cannot participate in the charge and discharge cycles, so that the performance is limited.

[0008] To overcome this effect, known methods include extending the electrolyte's action time, introducing the electrolyte under the effect of negative pressure, changing the electrolyte's composition to make it more fluid, and / or providing pores in the electrodes of the electrochemical accumulator. All these solutions have in common that they are complex, limit formulation flexibility and / or excessively reduce the energy density of the electrochemical accumulator. Summary of the invention

[0009] The object of the invention is to provide a possibility for improving the wetting properties of electrochemical accumulators.

[0010] According to the invention, this object is achieved by an electrode for an electrochemical accumulator, the electrode comprising a current collector foil having a coating region for an electrode coating, the coating region comprising an outer region and a central region. The outer region of the coating region is closer to the outer edge of the current collector foil than the central region of the coating region. The electrode coating has at least one electrolyte-conducting region in the outer region, the diffusion rate of the electrolyte of the electrochemical accumulator in the electrolyte-conducting region being higher than the diffusion rate in the electrode coating outside the electrolyte-conducting region.

[0011] The outer edge is that edge of the current collector foil which extends parallel to the longitudinal direction of the current collector foil and along which the current collector foil (and therefore also the electrode) is rolled up when the electrode is processed into an electrode coil or jelly roll.

[0012] The invention is based on the basic idea of ​​increasing the wettability of the electrode by the targeted introduction of electrolyte-conducting regions into the electrode coating, which allow the electrolyte to diffuse faster along these electrolyte-conducting regions than outside these regions. This creates, so to speak, an "electrolyte highway" in the electrode coating.

[0013] The improved wettability of the electrode according to the invention can be shown in comparison with conventional electrode coatings. For this purpose, two cells with the same electrode design, i.e. the same length and with the same electrode coating, are filled with an electrolyte of the same composition. The only difference between the two cells is that the conventional electrodes manufactured do not have the electrolyte conduction area according to the invention. The difference in the diffusion rate of the electrolyte can be represented by a stable or fluctuating, i.e. still elevated open circuit voltage (OCV value). By opening the cells, in cells not according to the invention, the differences can be found by different discolored areas on the electrodes or even local electroplating.

[0014] Outside the active cell, the lower coating edge of the dry comparison electrode can be placed in a glass with an electrolyte or a similar liquid as a flow medium, which can be doped with a colorant or contrast agent, for example. In this case, the flow medium front of the electrolyte moves at different speeds. If the movement of the flow medium cannot be confirmed visually, the comparison electrode can be further tested. For example, the movement distance of a specific solid added to the electrolyte or flow medium after a predetermined time can be confirmed by EDX analysis. For the EDX analysis, the liquid component of the flow medium is evaporated, while the added solid remains in the electrode.

[0015] The electrolyte-conducting regions are arranged in the region of the electrode coating, which in the later installed position of the electrode are assigned to the upper side or the lower side of the electrode coil, i.e., those regions which can be reliably supplied with electrolyte. In the case of the upper side of the electrode coil, the supply of electrolyte takes place by the electrolyte usually being filled from above into the battery housing of the electrochemical battery through a filling opening, while the lower side is supplied with electrolyte by the electrolyte flowing downwards between the electrode coil and the side of the housing under the effect of gravity.

[0016] The design of the electrode according to the invention ensures that, on the one hand, the diffusion rate of the electrolyte is influenced and thus also optimal wetting of the central region of the electrode coating can be achieved, while on the other hand, the energy density of an electrochemical accumulator having the electrode according to the invention is not excessively reduced, since adaptation to the electrode coating is only required in the electrolyte-conducting region. Thus, an optimal compromise between wettability and energy density can be achieved.

[0017] The electrolyte conducting region can be a partial region of the outer region. Alternatively, the entire outer region can also form the electrolyte conducting region.

[0018] The outer region in particular occupies 10% to 40% of the area of ​​the coated region of the current collector foil, while the remainder of the coated region is formed by the central region.

[0019] In one embodiment, the electrode coating comprises a fiber material in the electrolyte conducting region. The fiber material is used to transport the electrolyte through the electrode coating on or in the fiber material. In other words, the electrolyte is “conducted through” the electrolyte conducting region on the fiber material to a certain extent.

[0020] The fiber material may comprise or consist of glass fibers and / or cellulose fibers.

[0021] Conductive fiber materials can also be used. In this way, the electrical properties of the electrode coating can be influenced at the same time by the fiber material. As conductive fiber materials, metallized glass fibers or conductive carbon fibers, such as so-called "vapor-grown carbon fibers", can be used, for example.

[0022] In another embodiment, the electrode coating comprises a porous material that absorbs the electrolyte in the electrolyte-conducting region. In this case, the diffusion rate of the electrolyte is increased by the absorption effect caused by the porous material.

[0023] The term "absorbent" is understood herein to mean that the porous material is able to absorb the electrolyte into the pores of the porous material.

[0024] The porous material may be a carbon material. In particular, the carbon material is selected from carbon aerogel, mesoporous carbon, macroporous carbon, carbon prepared by template synthesis, and combinations thereof.

[0025] An example of a suitable carbon material is commercially available from Heraeus under the name "Porocarb".

[0026] The term "mesoporous carbon" herein refers to carbon materials with pore sizes ranging from 2 nm to 50 nm, while "macroporous carbon" is a carbon material with pore sizes greater than 50 nm.

[0027] Carbon materials can also have a hierarchical pore system, in which smaller pores with pore sizes in the nanometer range are located in the walls of larger pores with pore sizes in the micrometer range. For example, carbon materials with a hierarchical pore system are so-called "Kroll carbons".

[0028] In yet another design, the electrode coating has one or more depressions in the electrolyte-conducting region. The depressions provide defined voids on the surface of the electrode coating that can be filled with electrolyte. In other words, the depressions can serve as a kind of "collection container" for the electrolyte, from which the electrolyte can diffuse into other regions of the electrode coating.

[0029] The depression has in particular a substantially elongated outer contour which points from the outer edge of the current collector foil in the direction of the central region. That is, the depression has in particular a greater extension in this direction (also referred to as the width direction) than in a direction parallel to the outer edge (also referred to as the longitudinal direction).

[0030] For example, the extension of the depression in the width direction is at least twice as long as its extension in the longitudinal direction.

[0031] Preferably, at least one depression has an outer contour which tapers in the direction of a central region of the electrode coating.

[0032] In particular, the at least one depression can have a symmetrical outer contour.

[0033] The one or more depressions can also extend in a capillary-like manner from the outer edge in the direction of the central region through the outer region of the electrode coating.

[0034] In order to introduce the depressions into the electrode coating, the depressions can be produced after the electrode coating has been applied to the current collector by means of a roller having a structured surface.

[0035] In yet another configuration, the electrode coating comprises a pore former in the electrolyte-conducting region, wherein the pore former is configured to be at least partially removable from the electrode coating.

[0036] The pore formers make it possible to selectively produce pores in the electrode coating by removing the pore formers, which pores can be influenced in terms of their shape, size and position. In this way, the structure of the produced pores can be controlled particularly precisely to achieve an optimal compromise between reducing the energy density achievable with the electrode and the electrolyte absorption properties.

[0037] The pore former can be designed to at least partially, in particular completely, decompose into gaseous compounds when the decomposition temperature is reached. In this way, the pore former can be removed from the electrode coating after the decomposition temperature is reached.

[0038] For example, the pore former is ammonium bicarbonate (NH 4 HCO 3 ), which decomposes at 60°C or higher.

[0039] In particular, during the production of the electrode and / or the electrochemical storage cell using the electrode, the pore former can be converted into the gas phase (for example by vacuum drying or evaporation of the pore former). Thus, within the meaning of the present invention, conversion into the gas phase is possible even without chemical conversion.

[0040] Preferably, in a process step that is necessarily present in the corresponding production method, the pore former is simultaneously converted into the gas phase, so that no additional work step for removing the pore former is required. The pore former can be removed, for example, in a step of vacuum drying the electrodes before assembling the cell. If this step is performed, the vacuum drying temperature is >60°C.

[0041] If the electrode production is carried out without vacuum drying, the pore former can also be removed during the drying step of the entire cell.

[0042] Furthermore, the object of the invention is achieved by an electrochemical accumulator comprising at least one electrode as described above.

[0043] The features and properties of the electrode according to the invention apply correspondingly to the electrochemical storage cell and vice versa; for details, reference is made to the above description.

[0044] The electrochemical storage cell is in particular a lithium-ion battery, so that the invention relates in particular to an electrode for a lithium-ion battery and to a lithium-ion battery having such an electrode.

[0045] The term "lithium-ion battery" is used synonymously with all names commonly used in the prior art for primary battery components and cells containing lithium, such as lithium batteries, lithium-ion cells, lithium polymer cells and lithium-ion accumulators. In particular, rechargeable batteries (secondary batteries) are included. The terms "battery" and "electrochemical cell" are also used synonymously with the terms "lithium-ion battery" and "lithium-ion cell".

[0046] By using the electrode according to the invention in the electrochemical accumulator according to the invention, it is possible to wet the electrode coils of the electrochemical accumulator as completely as possible without unnecessarily greatly reducing the energy density of the electrochemical accumulator.

[0047] Improved wetting of the electrolyte also results in a more uniform heat release during operation of the electrochemical storage cell, which has a positive effect on the reliability and service life of the electrochemical storage cell.

[0048] Furthermore, the object of the present invention is solved by a method for manufacturing an electrode of an electrochemical battery as described above, the method comprising coating and / or treating an electrode coating on a coated area of ​​a current collector foil so that the electrode coating comprises different areas, wherein the different areas provide different diffusion rates for the electrolyte, wherein the different areas comprise at least one outer area and a central area.

[0049] In other words, the method is based on the basic idea of ​​influencing the composition and / or structure of the electrode coating in such a way that regions with different diffusion rates are produced.

[0050] In one variant, the composition of the electrode coating differs in different regions, namely in the outer region and in the central region.

[0051] For example, fibrous materials, porous materials and / or pore formers are added to the outer region or a suitable electrode coating is formulated which additionally contains the components.

[0052] To process the electrode coating, the electrode coating can be calendered using a roller having a structured roller surface.

[0053] The term “structured roller surface” is understood to mean a roller surface which has at least one protrusion, by means of which depressions can be produced in the electrode coating.

[0054] Thus, during the (usually present anyway) calendering step in electrode production, one or more depressions can also be simultaneously introduced into the outer region of the electrode coating.

[0055] Further features and characteristics of the invention emerge from the following description of exemplary embodiments and from the drawings, which description is not to be understood in a restrictive sense. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In the attached picture:

[0057] Figure 1 Schematically shows an electrode coil of an electrochemical battery having an electrode according to one embodiment;

[0058] Figures 2 to 4 Show Figure 1 Different embodiments of electrodes;

[0059] Figures 5 to 7 Similar to Figures 2 to 4 Shown Figure 1 Other embodiments of the electrode;

[0060] Figure 8 Schematic diagram for manufacturing Figure 1 The processing steps of a first embodiment of the method for an electrochemical storage cell;

[0061] Fig. 9 Schematic diagram of electrode precursors and electrodes, as they can be obtained from Figure 8 as obtained by the method of

[0062] Fig.10 Schematic diagram for manufacturing Figure 1 The processing steps of the second embodiment of the method for an electrochemical storage cell;

[0063] Fig.11 Schematically showing how Fig.10 A roller for use in the method; and

[0064] Fig.12 The electrodes are schematically shown as they can be obtained from Fig.10 as obtained by the method. DETAILED DESCRIPTION

[0065] Figure 1 The electrode coil 10 of an electrochemical storage cell 12 is schematically shown, wherein Figure 1 The illustration in shows the electrode coil 10 which is partially rolled up, so that the electrode 14 is partially visible.

[0066] The electrode coil 10 includes an electrode 14 , a counter electrode (not shown), and a separator (not shown) arranged between the electrode 14 and the counter electrode and electrically isolating the electrode 14 and the counter electrode from each other.

[0067] In principle, the electrode coil 10 may include a plurality of electrodes 14 and counter-electrodes, which are each electrically isolated from one another by a separator.

[0068] The electrode 14 includes an electrically conductive current collector foil 16 , which is formed, for example, from copper or aluminum.

[0069] The current collector foil 16 is covered by the electrode coating 20 , except for the contact-making region 18 in which the current collector foil 16 is exposed. In other words, the electrode coating 20 covers the coated region 22 of the current collector foil 16 .

[0070] The contact region 18 and the coated region 22 extend along the longitudinal direction x of the electrode coil 10 or the electrode 14 over their entire length, but are separated from one another along the width direction z, wherein the contact region 18 adjoins the coated region 22 .

[0071] The coated region 22 is in turn divided into an outer region 24 and a central region 26 , wherein the outer region 24 is located closer to an outer edge 28 than the central region 26 in the width direction z of the current collector foil 16 .

[0072] In the current collector foil 16 Figure 1 At the end shown at the bottom (which corresponds to the underside 30 of the electrode coil 10), the outer region 24 there directly adjoins the outer edge 28 in the width direction z, while at the current collector foil 16 Figure 1 At the end shown at the top, which corresponds to the top side 32 of the electrode coil 10 , the outer region 24 there is separated in the width direction z by the contact-making region 18 from the outer edge 28 there.

[0073] In the installed position of electrode coil 10 in electrochemical cell 12 , electrode coil 10 is accommodated in a cylindrical battery housing (not shown) having an upper cover with a filling opening for filling the battery housing with electrolyte 38 (see Figure 2 ).

[0074] When assembling electrochemical accumulator 12 , it is particularly important that electrolyte 38 penetrates electrode coil 10 as completely and uniformly as possible, since during operation of electrochemical accumulator 12 only the wetted parts of electrode coil 10 can participate in the charging and discharging process.

[0075] For this purpose, outer region 24 is designed as an electrolyte-conducting region 34 in which the diffusion rate of electrolyte 38 is higher than in the rest of electrode coating 20 .

[0076] Therefore, electrolyte 38 can diffuse faster in electrolyte-conducting region 34 in the direction of central region 26 , ie parallel to width direction z, than outside electrolyte-conducting region 34 .

[0077] In principle, the electrolyte-conducting region 34 may also comprise only a portion of the outer region 24 along the longitudinal direction x.

[0078] exist Figures 2 to 4 The electrodes 14 are shown along Figure 1 Schematic cross-sectional view of the cutting plane AA in FIG. Figures 2 to 4 Each of the figures in illustrative figures illustrates one embodiment of electrode 14.

[0079] exist Figure 2 In the illustrated embodiment, the electrode coating 20 includes a fibrous material 36 in the electrolyte conductive region 34 that extends through the electrolyte conductive region 34 along a width direction z.

[0080] The fiber material 36 is, for example, glass fibers and / or cellulose fibers.

[0081] The fiber material 36 provides a preferred transport path for the electrolyte 38 on its surface due to the interaction between the fiber material 36 and the electrolyte 38 (e.g. Figure 2 ), and in this way ensure a higher diffusion rate of the electrolyte 38.

[0082] Instead of or in addition to fiber material 36 , electrode coating 20 may include a porous material, such as a carbon material, that has adsorptivity for electrolyte 38 and in this way aids in the transport of electrolyte 38 through outer region 24 .

[0083] exist Figure 3 In the embodiment shown, each electrolyte conducting region 34 has depressions 40 introduced into the electrode coating 20 by a calendaring process, for example by a structured roller, as will be described in more detail below.

[0084] The depression 40 has an elongated geometry along the width direction z and tapers starting from the outer edge 28 towards the central region 26 .

[0085] Figure 4 The illustrated embodiment shows an electrode 14 obtained by using a pore former 42 .

[0086] The pore former 42 is designed to be removed from the electrode coating 20 during the production of the electrode 14 in order to form the pores 44 , for example by at least partially decomposing the pore former 42 into gaseous compounds after heating to a decomposition temperature.

[0087] In this way, the holes 44 are highly deformable in terms of arrangement, size and shape. Figure 3 In contrast to the embodiment of FIG. 4 , holes 44 can also be produced which are not adjacent to the boundary surface of electrode coating 20 .

[0088] As in Figure 4 As can be seen in the figure, the pore former 42 can also be only partially removed, so that residual pore former 42 still remains in the finished electrode coating 20. However, it is preferred that the pore former 42 is completely removed in the finished electrode 14.

[0089] It goes without saying that according to Figures 2 to 4 The embodiments can also be combined with one another, for example by combining a fiber material 36 , a porous material or a pore former with the depressions 40 .

[0090] Figures 5 to 7 Several embodiments of the electrode 14 are shown, which are similar to those according to Figures 2 to 4 In this case, however, an electrode coating 20 is applied on both sides of the current collector foil 16 , that is to say on the front side 46 of the current collector foil 16 as well as on the back side 48 thereof.

[0091] Figure 5 A configuration is shown in which the electrode coating 20 comprises a fiber material 36 in the outer region 24 . Figure 6 A configuration is shown in which the electrode coating 20 has a depression 40. Figure 7 A configuration is shown in which electrode coating 20 has pores 44 which were obtained by using a pore former.

[0092] Basically, it is also possible for the electrode coating 20 to be configured differently on the front side 46 and on the back side 48 of the current collector foil 16 . For example, the electrode coating 20 has the fiber material 36 on the front side 46 of the current collector foil 16 , while the electrode coating 20 has the depressions 40 on the back side 48 of the current collector foil 16 .

[0093] Figure 8 The process steps in the method according to the invention for producing an electrode 14 according to a first specific embodiment of the method are schematically illustrated.

[0094] The collector foil 16 is conveyed by means of conveying rollers 50 in the machine direction R, wherein the back side 48 of the collector foil 16 is in contact with the conveying rollers 50 . On the front side 46 , the electrode coating 20 is applied by means of a metering device 52 by applying an electrode mixture 53 in the central region 26 of the coating region 22 .

[0095] The electrode mixture 53 may differ from the electrode coating 20 in that, for example, additional solvent is included in the electrode mixture 53 to improve meterability.

[0096] The metering device 52 is fluidically connected to a supply device 54 which supplies the metering device 52 with an electrode mixture 53 .

[0097] Arranged downstream of the metering device 52 in the processing direction R are a plurality of additive metering devices 56 , 58 and 60 , which are each fluidically connected to an additive supply device 62 .

[0098] The outer region 24 of the current collector foil 16 is covered with an electrode coating 20 by the additive metering devices 56 to 60, wherein the electrode coating 20 in the outer region 24 is different from the electrode coating in the central region 26. Accordingly, the additive metering devices 56 to 60 can prepare one or more electrode mixtures 61, which are different from the electrode mixture applied by the metering device 52. For example, the electrode coating 20 in the outer region 24 has the fiber material 36 as described above.

[0099] Fig. 9 A schematic top view of an electrode precursor 65 is shown, as it can be obtained by means of the above method. As can be seen, the electrode precursor 65 has two central regions 26 and a total of three outer regions 24, wherein the outer regions 24 are each applied to the current collector foil 16 by means of one of the additive metering devices 56, 58 or 60.

[0100] The electrode precursor 65 is separated, for example cut, along the line S in a subsequent process step in order to obtain two electrodes 14 .

[0101] Fig.10 The processing steps in a second embodiment of the method according to the invention are shown schematically.

[0102] In this embodiment, the current collector foil 16 is provided with an electrode coating 20 both on its front side 46 and on its back side 48 in a preceding process step.

[0103] The coated current collector foil 16 is subsequently guided in the machine direction R through a roller pair having two rollers 64 in order to calender the electrode coating 20 and simultaneously provide the depressions 40 .

[0104] For this purpose, the two rollers 64 have a structured roller surface 66, as in Fig.11 The structured roller surface 66 has a plurality of protrusions 68 extending in concentric rings on the roller 64 .

[0105] The concentric rings are arranged such that they interact with the electrode coating 20 in the outer region 24 of the coated area of ​​the current collector foil 16 during calendering, so that depressions 40 are produced in the outer region 24 .

[0106] Fig.12 An electrode precursor 65 is schematically shown, as it can be obtained according to a second specific embodiment of the method.

[0107] By following Fig.12 By dividing the electrode precursor 65 along the line S in FIG. 1 , two electrodes 14 can be obtained again.

[0108] As can be seen, the elevation 68 of the roller 64 is shaped in such a way that the depression 40 tapers toward the central region 26 and is symmetrical about an axis extending perpendicularly to the outer edge 28 .

[0109] Overall, the electrode 14 is characterized in that, by targeted influencing of the electrode coating 20 , an optimum compromise between wettability with the electrolyte 38 and achievable energy density can be achieved.

Claims

1. An electrode (14) for an electrochemical storage cell (12), the electrode comprising a current collector foil (16) having a coating region (22) for an electrode coating (20), the coating region comprising an outer region (24) and a central region (26), wherein: The outer region (24) of the coated region (22) is closer to the outer edge (28) of the current collector foil (16) than the central region (26) of the coated region (22), and The electrode coating (20) has in the outer region (24) at least one electrolyte-conducting region (34), in which a diffusion rate of an electrolyte (38) of the electrochemical accumulator (12) is higher than a diffusion rate in the electrode coating (20) outside the electrolyte-conducting region (34).

2. The electrode (14) according to claim 1, wherein: The electrode coating (20) comprises a fibrous material in the electrolyte conducting region (34).

3. The electrode (14) according to claim 1 or 2, wherein: The electrode coating (20) comprises a porous material that is absorbent to an electrolyte (38) in the electrolyte conducting region (34).

4. The electrode (14) according to any one of the preceding claims, wherein The electrode coating (20) has one or more depressions (40) in the electrolyte conducting region (34).

5. The electrode (14) according to claim 4, wherein: At least one of the depressions (40) has an outer contour that tapers toward a central region (26) of the electrode coating (20).

6. The electrode (14) according to any one of the preceding claims, wherein The electrode coating (20) includes a pore former (42) in the electrolyte conducting region (34), the pore former being configured to be at least partially removable from the electrode coating (20) upon forming one or more pores (44) in the electrode coating (20).

7. An electrochemical accumulator (12) comprising at least one electrode (14) according to any one of the preceding claims.

8. A method for producing an electrode (14) according to any one of claims 1 to 6 for an electrochemical storage cell (12), the method comprising applying and / or treating an electrode coating (20) on a coating region (22) of the current collector foil (16) so that the electrode coating (20) comprises different regions which provide different diffusion rates for an electrolyte (38), wherein: The different regions include at least an outer region (24) and a central region (26).

9. The method according to claim 8, wherein: The composition of the electrode coating (20) is different in the different regions.

10. The method according to claim 8 or 9, wherein: The electrode coating (20) is calendered using a roller (64) having a structured roller surface (66).

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